For example, as techniques for forming circuit patterns on a circular disk-shaped substrate in the course of manufacturing semiconductor devices, there is known a film formation process sequence and a photolithography process sequence. According to these process sequences, a film formation process and a cleaning process are repeatedly performed on the substrate.
In cleaning and drying processes of this kind, a substrate gripping device is used (for example, see Japanese Patent No. 4681148). This substrate gripping device includes a rotary table provided therein for driving rotation. The rotary table is equipped with a plurality of pin bases on its outer peripheral part such that each of them is revolvable about an axis parallel with the rotational axis of the rotary table.
A chuck pin is protruded at an eccentric position on the upper surface of each of the pin bases. This chuck pin has a receiving surface slanted downward toward the center of the rotary table.
These pin bases are configured to be rotationally driven in the same direction by a driving means. Accordingly, when the pin bases are rotated in a predetermined direction to eccentrically rotate the chuck pins, the receiving surfaces of the chuck pins are brought into contact with the bottom side of the substrate at its outer edge portions, so that the rotary table integrally grips a substrate.
When a substrate is processed, the rotary table is rotated along with the substrate gripped thereon, while a process liquid is sprayed onto the process target surface of the substrate. The process liquid flows in the radial direction of the substrate by the rotation of the rotary table, and the process target surface of the substrate is thereby processed. However, the process liquid cannot flow at the positions where the chuck pins are in contact, and so unprocessed portions are generated on the substrate. As a countermeasure for this problem, there is known a method that rotates the chuck pins to change the gripping positions, or a method that provides two chuck pins on each of the pin bases and switches these chuck pins when gripping the substrate (for example, see Japanese Patent No. 3955176 and Japanese Patent No. 3762275). In the case of the method that uses the two chuck pins for re-gripping, the switching is performed while the substrate is supported by substrate support pins from the bottom side of the substrate. Other than these methods, there is known a method that causes the substrate to slide on the receiving surfaces of the chuck pins by use of acceleration and deceleration of the rotary table.
After the predetermined process is performed on the substrate, the pin bases are rotated in the direction opposite to the predetermined direction mentioned above to cancel the gripping state of the substrate, so that the substrate can be taken out of the rotary table.
However, the substrate gripping device described above has the following problems. Specifically, in the case of the method that rotates the chuck pins to change the gripping positions, the substrate may slide if the gripping force is not larger than a certain level, and so it is difficult to judge whether the position change has been certainly performed. Further, this method needs to incorporate a mechanism for rotating the chuck pins while rotating the substrate, and the structure of the device thereby becomes complicated as a whole.
In the case of the method that uses the two chuck pins for re-gripping, the substrate support pins are brought into contact with the bottom side of the substrate. However, when the substrate reverse side is processed, this substrate reverse side needs the pins to be out of contact therewith, and so this method is not applicable to the reverse side process. In addition, the rotary table needs to once stop rotation when performing the chuck pin switching, and the process time is thereby prolonged. Further, other than the rotational drive mechanism of the rotary table, a switching mechanism for the two chuck pins is required, and the structure is thereby complicated.
In the case of the method that causes the substrate to slide on the receiving surfaces of the chuck pins, it is necessary to apply an inertia force not smaller than the friction force between the substrate and the receiving surfaces of the chuck pins. However, this friction force varies depending on the end portion shape and/or surface state of the substrate and the process steps, and so it is difficult to stably perform the operation.